2. • Nystagmus is an involuntary oscillation of the eyes that can be a physiological (e.g. following the rotation of an optokinetic drum)
or pathological phenomenon. In pathological nystagmus, each cycle of movement is usually initiated by an involuntary, defoveating drift of the eye away from the target, followed by a refixating saccadic movement.
• Plane may be horizontal, vertical, or torsional.
• Amplitude refers to the extent of excursion: fine or coarse.
• Frequency describes how rapidly the eyes oscillate: high,
moderate or low.
• Classification
• Jerk nystagmus is saccadic with a slow defoveating ‘drift’ movement and a fast corrective refoveating saccadic movement. The direction of nystagmus is described in terms of the direction of the fast component: right, left, up, down or rotatory.
• Pendular nystagmus is non-saccadic in that both the foveating and defoveating movements are slow (i.e. the velocity of nystagmus is equal in both directions).
• Mixed nystagmus consists of pendular nystagmus in the primary position and jerk nystagmus on lateral gaze.
3. • Physiological nystagmus
• End-point nystagmus is a fine jerk nystagmus of moderate frequency seen in extremes of gaze. The fast phase is in the direction of gaze.
• Optokinetic nystagmus (OKN) is a jerk nystagmus induced by moving repetitive targets (e.g. OKN drum) across the visual field.
• The slow phase is a pursuit movement in which the eyes follow the target. The fast phase is a saccadic movement in
the opposite direction as the eyes fixate on the next target.
• If the OKN tape or drum is moved from right to left, the left parieto-occipito-temporal region controls the slow (pursuit) phase to the left and the left
frontal lobe controls the rapid (saccadic) phase to the right.
• OKN nystagmus is useful for detecting functional (non-physiological) blindness and for testing VA in the very young. It can be helpful in the
assessment of an isolated homonymous hemianopia.
• Vestibular nystagmus
• Physiological vestibular nystagmus is a jerk nystagmus caused by altered input from the vestibular nuclei to the horizontal gaze centres. The slow phase
is initiated by the vestibular nuclei and the fast phase by the brainstem and frontomesencephalic pathway. Vestibular nystagmus may be elicited by caloric
stimulation as follows:
• When cold water is poured into the right ear the patient will develop left jerk nystagmus (i.e. fast phase to the left).
• When warm water is poured into the right ear the patient will develop right jerk nystagmus (i.e. fast phase to the
right). A useful mnemonic is ‘COWS’ (cold-opposite, warm-same) indicating the direction of the nystagmus.
• When cold water is poured into both ears simultaneously, a jerk nystagmus with the fast phase upwards develops. Warm water in both ears elicits
nystagmus with the fast phase downwards (cold ‘slows things down’).
• An abnormal test indicates the presence of peripheral vestibular disease.
• • Pathological peripheral vestibular nystagmus (Fig. 19.88) is caused by disease affecting the ear such as labyrinthitis, Ménière disease and middle
or inner ear infections. It tends to be solely horizontal, vertical or torsional, increases in intensity with gaze in the direction of the fast phase and is
dampened by fixation. It is typically of fine amplitude
4. Infantile (congenital) nystagmus
Introduction
Early-onset (usually the first few months of life rather than truly congenital) nystagmus can occur secondary to poor vision or to a motor deficit with the
nystagmus itself causing poor vision, though the distinction is not always clear. It can be associated with a serious systemic condition, particularly of the
central nervous system. Infantile nystagmus is commonly pendular but may be jerk, horizontal and uniplanar (direction of oscillation remains constant
regardless of direction of gaze). In contrast to adults with acquired nystagmus, oscillopsia is not experienced even by adults with congenital nystagmus.
The nystagmus may be dampened by convergence and is not present during sleep. There is usually a null point – a position of gaze in which nystagmus is
minimal – and a compensatory head posture may develop to favour this. Investigation should seek to detect ocular and systemic association
Sensory deficit (afferent) nystagmus
Sensory deprivation nystagmus is the more common form of infantile nystagmus and is caused by impairment of central vision in early life (e.g. congenital
cataract, macular hypoplasia, albinism, Leber congenital amaurosis, optic nerve hypoplasia, achromatopsia). In general, children with bilateral poor vision
under 2 years of age develop nystagmus, the severity of which is associated with the degree of visual loss.
Congenital motor (efferent) nystagmus
A family history is common, with X-linked (dominant or recessive) inheritance the common mode. Presentation is about 2–3 months after birth and persists
throughout life. VA is generally better than with sensory deficit nystagmus, at 6/12–6/36. In the primary position there is low-amplitude pendular nystagmus
that may convert to jerk nystagmus on side gaze
Spasmus nutans
Presentation of this rare condition is between 3 and 18 months with unilateral or bilateral small-amplitude high-frequency horizontal nystagmus (Fig. 19.90)
associated with head nodding. It is frequently asymmetrical, with increased amplitude in abduction. Vertical and torsional components may be present. An
idiopathic form spontaneously resolves by age 3 years, but glioma of the anterior visual pathway, empty sella syndrome and porencephalic cyst can also
be causative.
Others
Other forms of nystagmus such as periodic alternating (see below) can be infantile in presentation.
5. Acquired nystagmus
Latent nystagmus
Latent nystagmus is associated with infantile esotropia and dissociated vertical deviation (see Ch. 18). With both eyes open there is no nystagmus, but
horizontal nystagmus becomes apparent on covering one eye; the fast phase is in the direction of the uncovered fixating eye. Occasionally an element of
latency may be superimposed on a manifest nystagmus so that when one eye is covered the amplitude of nystagmus increases (manifest-latent nystagmus).
Periodic alternating nystagmus
Periodic alternating nystagmus (PAN) is a conjugate horizontal jerk nystagmus that periodically reverses direction. During the active phase, the amplitude and
frequency of nystagmus first progressively increase then decrease. This is followed by an interlude lasting 4–20 s during which time the eyes are steady and
may show low-intensity, often pendular movements. A similar sequence in the opposite direction occurs thereafter, the whole cycle lasting between 1 and 3
minutes. PAN can be congenital or due to cerebellar disease, ataxia telangiectasia and drugs such as phenytoin.
Convergence–retraction nystagmus
Convergence–retraction nystagmus is a jerk nystagmus due to the co-contraction of extraocular muscles, often the medial recti. It can be induced by rotating an
OKN drum downwards; the upward refixation saccade brings the two eyes towards each other in a convergence movement. There is classically associated
retraction of the globe into the orbit. It is a component of Parinaud dorsal midbrain syndrome (see Fig. 19.84). Causes include lesions of the pre-tectal area such
as pinealoma and vascular accidents.
Downbeat nystagmus
This is a vertical nystagmus with the fast phase beating downwards (Fig. 19.91), more easily elicited in lateral gaze and downgaze. It can be caused by lesions
at the foramen magnum such as Arnold–Chiari malformation and syringobulbia, drugs such as lithium and phenytoin and a range of other conditions such as
Wernicke encephalopathy, demyelination and hydrocephalus.
Upbeat nystagmus
Upbeat nystagmus is a vertical nystagmus with the fast phase beating upwards in all positions (Fig. 19.92); causes include posterior fossa lesions, drugs and
Wernicke- encephalopathy.
See-saw nystagmus
A pendular nystagmus, in which one eye elevates and intorts while the other depresses and extorts. It can be due to parasellar tumours (often with bitemporal
hemianopia), syringobulbia and brainstem stroke.
Ataxic nystagmus
Ataxic nystagmus is a horizontal jerk nystagmus that occurs in the abducting eye of a patient with an INO (see above).
Bruns nystagmus
This consists of a coarse cerebellar horizontal jerk nystagmus in one eye and fine high-frequency vestibular nystagmus in the other and can be caused by
cerebellopontine angle tumours such as acoustic neuroma.
6. Treatment of nystagmus
• Amblyopia and refractive error should be managed as appropriate. Contact lenses and other refractive measures such as the combination of high minus
contact lenses and high plus spectacle lenses may be helpful.
• Medication such as baclofen and gabapentin may be helpful. • Botulinum toxin injection into the extraocular muscles has had some success but can be
unpredictable and long-term treatment is required.
• Surgery for nystagmus with a null point is aimed at moving muscles in order to mimic muscle tension while the eyes and face are straight and may be
performed to address a compensatory head posture. Recession of all horizontal recti has been successful in reducing the amplitude of nystagmus in some
patients without a significant null point.
Nystagmoid movements
Nystagmoid movements resemble nystagmus, but the initial pathological defoveating movement is a saccadic intrusion.
Ocular flutter and opsoclonus
These entities consist of saccadic oscillations with no intersaccadic interval; in ocular flutter oscillations are purely horizontal and in opsoclonus they are
multiplanar. Causes include viral encephalitis, myoclonic encephalopathy in infants (‘dancing eyes and dancing feet’), as a transient idiopathic occurrence in
healthy neonates, or may be drug-induced.
Ocular bobbing
Ocular bobbing manifests with rapid downward conjugate eye movements with a subsequent slow drift up to the primary position. Causes include pontine
lesions (usually haemorrhage), cerebellar lesions compressing the pons and metabolic encephalopathy.
Superior oblique myokymia
Superior oblique myokymia is a rare condition characterized by intermittent episodes of oscillopsia and diplopia in one eye (usually the right eye). The cause is
not known, but the condition may follow ocular or head injury and rarely brainstem tumours. Some cases occur secondary to compression of the trochlear nerve
root by the adjacent superior cerebellar artery, resulting in ephaptic impulse transmission. There is no definitive treatment, but oral or topical beta-blockers can
be helpful. In persistent cases, superior oblique muscle weakening procedures may be tried. It should be distinguished from orbicularis oculi muscle
myokymia (tic) which is common, innocuous and usually settles spontaneously.
